The present invention relates generally to packaging, and more particularly, to a packaging for components of an optical module that employs a flexible circuit with two stiffeners packaging.
An optical module includes components for performing the functions of the optical module. One common optical module is the optical transmitter. The primary function of the optical transmitter is to translate electrical signals into corresponding optical signals. The major components of an optical transmitter are a laser (e.g., a vertical cavity surface emitting laser (VCSEL)) and one or more integrated circuits for driving the VCSEL and controlling the functions of the optical transmitter. The optical module interfaces with an external circuit (e.g., a printed circuit board of a switch or router) to receive data signals that need to be converted into corresponding optical signals.
As can be appreciated, the components in an optical module need to be arranged and packaged in such a manner as to efficiently interface with (1) the source of data signals, and (2) the optical medium (e.g., the fiber optic cable). One problem that the packaging must address is the bending of light.
The bending of light problem is related to the orientation of the external circuit with respect to the fiber optic cable and the optical module. The external circuit typically lies in a first plane. The optical module couples to the external circuit and is generally parallel to the first plane. Unfortunately, the VCSEL emits light in a generally perpendicular direction from the first plane, and the optical link (e.g., fiber optic cable) is generally disposed parallel to the first plane. Consequently, the light emitted from the VCSEL. must be bent about 90 degrees in order to interface with the optical link. In addition to solving this problem, it is desirable for the components of the optical module to have a packaging that arranges the components in an efficient manner, that is efficient to assemble, and that can be assembled reliably across variations in process and assembling technique.
A first prior art approach packages the laser on the same plane near the other circuit components, such as the laser driver integrated circuit, in order to improve the electrical performance of the system. This approach requires optics to bend the light about ninety degrees so that the light emitted by the laser can be directed into the fiber optic cable.
Regrettably, this prior art approach suffers from several disadvantages that stem primarily from the difficulties of processing the optical components needed to bend the light by about ninety degrees. First, the components utilized to bend the light need to be optically aligned with each other and with the laser. Since the alignment can vary across different processes, alignment of these components can become a severe challenge. This disadvantage is further exacerbated when there are multiple lasers (e.g., an array of VCSELs in a parallel multichannel optical module) Second, the optical interface of each of the components must be polished and cleaned so that the loss of light through each component is minimized. Unfortunately, the polish and clean steps require added costs to the process and injects processing complexities. Consequently, there are many difficulties in assembling a package that uses optical elements to bend the output light beam.
A second prior art approach packages the laser to optically couple with the fiber optic cable without using additional optics. In order to direct the light from the laser without bending optics, the laser is placed in a plane that is generally perpendicular to the plane of the other electrical components, such as the laser driver circuit. Wires are then employed to make the 90 degree turn and to connect the laser to the laser driver.
Although the second approach avoids the difficulties of using optics to bend the light, this approach unfortunately suffers from the following disadvantages. First, the electrical performance of the wires used to connect the laser to the laser driver is often poor due to the length of the wires, thereby leading to slower signal propagation speeds. The electrical performance is of particular concern for high-speed applications. Consequently, it is desirable to decrease the length of the wires, and thus, the distance between components in the system in order to increase the speed of the signal propagation. Second, the second prior art approach typically requires three-dimensional assembly of components. Consequently, it is desirable to simplify the manufacturing and assembly process.
Furthermore, the trend is that the number of optical module component is increasing due to multiple optical transmitters or receivers being assembled into a single optical module package. Unfortunately, at the same time the physical dimensions or size of the optical module are decreasing. Consequently, there is a need for packages to address this trend and to effectively assemble these additional components in an efficient manner without sacrificing signal integrity and process or assembly efficiency.
Based on the foregoing, there remains a need for a package that conveniently couples to an external circuit disposed in a first plane, that houses a laser and electronic components, and that ensures that light transmitted from the laser is oriented in a direction that is generally parallel to the first plane and that overcomes the disadvantages set forth previously.
According to one embodiment of the present invention, a packaging for components of an optical module is provided. The packaging includes a flexible circuit coupled to two stiffeners. The packaging has a first sub-assembly with the first stiffener for receiving a first component (e.g., a VCSEL laser array and an associated laser driver circuit). The packaging also has a second sub-assembly with the second stiffener for receiving a second component (e.g., a memory circuit) and for coupling to an external circuit (e.g., a printed circuit board of a network device). The packaging has a flexible portion with a first end for coupling the first sub-assembly and a second end for coupling to the second sub-assembly. The flexible portion allows the first sub-assembly to be oriented with respect to the second sub-assembly to form an angle that is greater than zero degrees and less than 180 degrees.
According to one aspect of the present invention, the packaging provides a mechanism (e.g., a flexible portion) for allowing or enabling a laser to emit light with an orientation that is generally parallel to the plane of an external circuit without optics for bending the light.
According to another aspect of the present invention, the packaging of the present invention includes a flexible circuit coupled to two stiffeners. The packaging includes a first sub-assembly having an integrated circuit receiving area that can receive a first integrated circuit and a second sub-assembly having an integrated circuit receiving area that can receive a second integrated circuit. A flexible circuit has at least one conductive trace to communicate signals between first integrated circuit in the first sub-assembly and the second integrated circuit in the second sub-assembly.
In the preferred embodiment, the first sub-assembly packages a VCSEL array and a VCSEL driver and the second sub-assembly packages a memory (e.g., an EEPROM) and provides a connection (e.g., BGA solder bumps) to an external circuit. The first and second stiffeners are fixably secured to a first and second surface of a heat sink in such a manner as to orient the first sub-assembly with respect to the second sub-assembly to form an angle of about 90 degrees. This arrangement disposes the VCSEL array in close proximity to the VCSEL driver so that the electrical performance and signal propagation speed are enhanced. Furthermore, this arrangement allows light to be directed from the laser array to the fiber optic cable without the need for optics for bending the light.